The present invention relates to lacquer coating compositions and, more particularly, to lacquer coating compositions containing vinylidene chloride polymers.
In recent years, vinylidene chloride polymer lacquers or solutions have been widely used, particularly in the food industry, as coatings for plastic films, cellophane and like packaging materials due to their high resistance to chemicals and oils, low temperature heat-sealing properties, and excellent resistance to the transmission of oxygen and moisture vapor.
Nevertheless, the linear vinylidene cloride polymers which are presently being used in such lacquers have exhibited a number of chronic problems which reduce the desirability of coatings prepared therefrom. In the first instance, it is difficult to control the molecular weight and composition distribution of the polymers, which leads to uncontrollable variations in heat-seal temperature and permeability. In addition, most of the comonomers which have been used to prepare such polymers react at a rate faster than vinylidene chloride, thereby leading to extensive composition drift both in bath and continuous addition emulsion polymerization. Such composition drift to higher and higher vinylidene chloride content results in vinylidene chloride fractions which are metastable in the lacquer solution. These metastable fractions tend to crystallize in the lacquer solution and cause problems with haze in the resulting coatings.
Accordingly, it is an object of the present invention to provide a vinylidene chloride polymer lacquer coating composition which avoids the above-mentioned problems.